1Field of the Invention
This invention relates to a liquid friction coupling, which comprises a housing that contains a viscous liquid, a shaft protruding into said housing, alternating and interdigitating inner and outer blades which are axially slidably and non-rotatably connected to the shaft and to the housing, respectively, annular expanding springs, which extend between adjacent inner blades or outer blades, and an annular piston, which is sealed in the housing and axially therein and is operable from the outside and arranged to act on the blades in order to change the blade spacing.
2. Description of the Prior Art
Such a liquid friction coupling is already known from Austrian Patent Specification No. 384,086 and the corresponding U.S. Pat. No. 4,844,219, the disclosure of which is incorporated herein by reference. In that known coupling the width of the gaps between adjacent inner and outer blades can be changed to control the slip of the speed of the driven part of the coupling because the coupling effect and/or the torque being transmitted is approximately inversely proportional to the width of the gap. But it has been found that the control range is relatively small in practice particularly because it has not been taken into account in the known proposal that the free space within the housing should be minimized. Besides, even when the blade spacing is large the gaps between adjacent inner and outer blades will always contain liquid so that torque will still be transmitted. For this reason a motor vehicle which has two driven axles and is provided with such a coupling often requires additional means for interrupting the power train extending between the axles if an improved handling of the vehicle is to be ensured during braking.